Yes, you can but you need a workstation class video card that is generally geared towards 3D rendering and an expensive professional H-IPS or S-PVA monitor specifically designed for graphic artists that has a color look-up table (LUT) to be able choose from more than 16.7m colors.
ATI FireGL series workstation video cards can support 40-bit and 64-bit color. nVidia Quadro workstation cards do not support those high bit colors.
Like I stated, you'll need a workstation class graphics card and the appropriate monitor.
For games it should not make a difference since games don't use above 32-bit color. To put it another way if you are watching a black and white movie on a color TV, the movie is still going to be black and white when you watch it.
during benchmark test in lost planet (trial), i got 64 bit depth with the same hardware, so looks like dx 10 can make it to 64 bit, and so i think dx11 may make it to 128bit (only guessing)
that means hd6670 can make it to 64bit in game (as game shows an option for it), but why not for desktop screen, i.e, why it shows only upto 32 bit depth as an option
is there any patch, software or setting for window 7 to make it to 64bit all the time
Why you need 64-bit? As long as you are not professional workers having FirePro there is no need of 64-bit colour depth. For me 32 is enough and there is no need more. Maybe 16-bit isn't enough but 32-bit is completely enough for me.
OK, but why? There is no need seriously if you are not professional worker as I said before.
yeah. Their is no need for me for it currently,
but if my hardware is capable of that thing then their is nothing bad to give it a try
also i am curious to know all capabilities of the hardware and how to use them.
No you probably can't these days with geforce or radeon cards. You may wait 2 or 3 years to wait for new windows and cards series to get 64-bit colour depth. I know your hardware is capable, but if you don't need it, why you are forcing yourself to make it? If you want to know how your hardware capabilities are maybe you should try other things instead of this colour dept. Because there is no such currently I think.